Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology may use a plurality of electrostatic actuators, piezoelectric actuators, or thermal actuators to eject ink from a plurality of nozzles in an aperture plate. In electrostatic ejection, each electrostatic actuator, which is formed on a substrate assembly, typically includes a flexible diaphragm or membrane, an ink chamber between the aperture plate and the membrane, and an air chamber between the membrane and the substrate assembly. An electrostatic actuator further includes an actuator electrode formed on the substrate assembly within the air chamber. When a voltage is applied to activate the actuator electrode, the membrane is drawn toward the electrode by an electric field and actuates from a relaxed state to a flexed state, which increases a volume of the ink chamber and draws ink into the ink chamber from an ink supply or reservoir. When the voltage is removed to deactivate the actuator electrode, the membrane relaxes, the volume within the ink chamber decreases, and ink is ejected from the nozzle in the aperture plate.
The air chamber for each electrostatic actuator across the printhead may be sealed or open to the atmosphere. A vented air chamber is typically preferred so that pressure within the air chamber and the atmosphere are equalized to decrease the effect of changing atmospheric pressure and temperature on the operation of the electrostatic actuators. For example, U.S. Pat. No. 8,567,911, commonly assigned herewith and incorporated herein by reference in its entirety, discloses an electrostatic actuator device having channels that vent the air chamber of each electrostatic actuator to the atmosphere.
Although venting the air channels to atmosphere makes a printhead more robust relative to elevation or air pressure changes, it makes the printhead less robust to changes in humidity since high humidity air entering the printhead changes the air breakdown properties which can impact the operation of the electrostatic actuator. The electrostatic actuators may behave increasingly erratic as humidity increases. An electrostatically actuated ink jet printhead having a more stable operation at changing environmental conditions would be desirable.